Effects of transfection of human beta-nerve growth factor gene on substance P and calcitonin gene-related peptide content of the spinal cord in a rat model of neuropathic pain

Objective To investigate the effects of adenovirus containing human beta-nerve growth factor (Ad-hNGFβ) gene on substance P (SP) and calcitonin gene-related peptide (CGRP) content of the spinal cord in a rat model of neuropathic pain by chronic constrictive injury (CCI). Methods Forty-eight male SD rats weighing 200-250 g were randomly divided into 3 groups (n=16 each) : group Ⅰ sham operation; group Ⅱ CCI and group Ⅲ CCI + Ad-hNGFβ gene IT. The animals were anesthetized with intraperitoneal choral hydrate 300-350 mg/kg. The right sciatic nerve was exposed and 4 ligatures were placed on the sciatic nerve at 1-2 nun intervals as described by Bennet and Xie[5]. In sham operation group, right sciatic nerve was exposed but not ligated. In group Ⅰ and Ⅱ artificial cerebrnspinal fluid was injected IT instead of Ad-hNGFβ gene. The behavior score and the paw-withdrawal latency (PWL) to radiant heat and mechanical stimulus were measured one day before operation and every 4 days within the 28 days after gene transfection. Four animals were killed at 4, 7, 14 and 28 day after IT gene transfection in each group and lumbar segment (L4-6 ) of the spinal cord was removed for determination of SP and CGRP content by immunohistochemistry. Results The behavior scores were significantly higher and PWL to radiant heat and mechanical stimulus were significantly lower in group Ⅱ and Ⅲ than in group Ⅰ. There was no significant difference in the behavior score and PWL to mechanical stimulus between group Ⅱ and Ⅲ while the PWL to radiant heat was significantly higher in group Ⅲ than in group Ⅱ. After operation SP and CGRP content were significantly higher in group Ⅱ and group Ⅲ than in group Ⅰ , and significangly lower in group Ⅲ than in group Ⅱ 7-28 days after operation. Conclusion The recomhinant Ad-hNGFβ gene transfection can attenuate heat hyperalgesia by reducing SP and CGRP content of the spinal cord in a rat model of neuropathic pain induced by CCI. Key words: Nerve growth factor;  Injections, spinal;  Transfection;  Neuropathic pain;  Substance P;  Calcitonin gene-related peptide